UCD School of Civil

Engineering.

2nd Hanrahan Memorial Lecture- 25th April 2018

Geotechnical properties of Irish compressible soils

Mike Long

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Edward (Eamon) T. Hanrahan

1917 - 2012

Books for An Foras Forbartha

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My approach to the task

• Starting with Hanrahan (1979) update Irish

experience

• What have we learned?

• What do we need to work on / future research?

• Modern techniques

• Resource for younger engineers

• Focus of presentation own research

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Acknowledgments

• Former MEngSc and PhD students (I. Lydon, E.

Conaty, G. Coy, C. Ruiz, S. Donohue, N. Boylan,

R. Carroll

• Colleagues in ARUP

• Colleagues in NGI and NTNU

• David Gill / Fintan Buggy

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Mentors

Michael Creed UCC

Nick O’Riordan

ARUP 58th Rankine

Lecturer 2018

David Hight GCG

38th Rankine Lecturer 1998

Tom Lunne NGI

Nilmar Janbu NTNU

25th Rankine Lecturer 1985

Rolf Sandven

NTNU and Multiconsult

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Important contributions since 1979

1996 2007 2012

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Content

• Background geology

• Complexity of deposits

• Hanrahan’s “troublesome” soils :alluvium,

estuarine and lake-bed soils (peat)

• Benchmarked against Norwegian clays

• Summary of well characterised sites / lessons

learned from construction

• SI techniques reviewed

• Sample disturbance effects

• Undrained shear strength

• 1D compression parameters

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Complexity of Irish compressible soils

• Macro-scale issue

• Micro-scale effects

• Contrast to Norwegian soft soils

• Message: be careful – significant GI often

warranted

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Fort Henry Embankment – Shannon Scheme

Photo courtesy Senan Mc Evoy - ESB

Fort Henry embankment 2.7 km, 8.5 m high 2 significant failures

90 years of monitoring data Physically inspected daily

Best monitored structure in Ireland? Complex alluvial ground conditions

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Study sites and lessons learned

• Study sites

• Construction techniques used

• Lessons learned

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Study sites

o 40 well characterised sites

o 3 groups o Considerable body of

valuable data

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Construction techniques used

o Number of excavate and replace cases underestimated

o Surcharging with vertical drains dominates

o Surcharging without vertical drains on 4 silt sites

o Eight recorded cases of piled embankments (not included)

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Lessons learned

o Primary compression predicted well

o Rate of primary compression often underestimated (cv or ch)

o Some cases when it is overestimated

o Smearing of vertical drains?

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o Importance of pc'

o Creep settlements significant issue

o Five significant failures (su)

Focus of remainder of paper

• What you will learn (hopefully!) in order to deal

with lessons learned

o Need samples but sampling in Irish soft soils is

very tricky

o CPTU very powerful technique. But…

o Other in situ techniques such as geophysics can

be useful

o Parameters such as su, pc‘, cv and Csec need to be

derived with care

o Gaps in our knowledge / further work warranted

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Details of some selected sites

• Post-glacial lake-bed clays

o Athlone Bypass

o Clonmore Road, Mullingar

• Alluvial soils

o Fort Henry Embankment – Shannon Scheme

• Silts

o Foynes Harbour Access Road

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Athlone Bypass

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Athlone Bypass – Profile D

o Complex conditions o Soils very soft o Sites need significant GI

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o dispersed arrangement of clay plates with silt grains

o some agreggations o random honeycombed / open

structure o no evidence of organics

SEM Athlone brown laminated clay

Image courtesy

Yoko Tanaka

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Clonmore Road, Mullingar (Joe Dolan Bridge)

Photos courtesy Michael Kelly Westmeath Co. Co.

Mullingar

Lough Ennell

Work by Westmeath Co. Co., IGSL, Fugro, AGL, Roughan and O’Donovan, Fehily Timoney Gifford

Lacy’s canal

River Brosna

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Clonmore Road – ground model

o Deepest well characterised site in Ireland? o Peat / calc marl up to 11.5 m o Soft ground to 28 m +

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Alluvial silts - SEM Sligo

Coy (2002)

o chaotic arrangement of silt particles

o porous calcitic matrix o organic structures o some large pores

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Foynes Harbour access road (silt or clay?)

o 15% clay content separating “silt” & “clay” like behaviour (NGF, 2011)

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Two distinct strata upper sandy

silt and lower clayey silt

Site Investigation Techniques

• Shell and auger drilling / instability at base of

S&A boreholes

• Sampling (piston, MOSTAP, block)

• CPTU

• Full flow probes

• SDMT / DMT

• Advanced drilling rigs

• Geophysics - shear waves – resistivity

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Shell and Auger drilling / piston sampling

Shell and auger drilling Sligo – Collooney Bypass

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Ballinasloe research site

U4 / U100 – not focus here

o Stress in soil beneath base of borehole

o Disturbance?

Instability at base of borehole

o Drilling mud often used to prevent failure at base

o Must have drilling mud > 1.25 water to prevent failure (OCR = 1 clays)

o In Ireland no drilling mud is used and holes often not kept topped up with water

o Possibility of failure is high

o Sampling in material either highly strained or even already failed

Perfect sampling

Failure

Requirement

Ladd and DeGroot (2003)

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ELE 100, D = 100 mm, AR = 6.8%, = 30° Modified ELE 100, = 5°

ENISO 22475-1 (2006) requires AR < 15% and = 5°

Sharp cutting edge angle is key

Piston sampling

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MOSTAP®

MOSTAP-65, D = 65 mm, AR = 105%, = 15°

MOSTAP-70, D = 70 mm, = 6°

Done in conjunction with CPT Cone head released at required depth before pushing tube NB: No borehole required

A.P. van den Berg

MOSTAP 65 sampling at Athlone

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Sherbrooke block sampling at Athlone

350 mm

250 mm

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CPTU

u2 qt

fs 10 cm2 cone

o Most widely used technique in soft soil in the world

o Powerful tool and will give valuable data

o Provided NB: filter is saturated

o Appropriate checks and corrections made

o European Standard (ENISO 22476-1, 2007)

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Typical CPTU results

Onsøy – van den Berg (u2)

Class 1 requirements qt = 0.035 MPa fs = 5 kPa u2 = 0.01 MPa

Clonmore Rd. – Fugro (u1)

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Comparative CPTU testing at Onsøy

Need to take care when using fs, e.g. soil behaviour charts, Ic etc. (Robertson)

Lunne e

t al. (

2018)

fs: most scatter values Class 1

u2: little variation

qt: some variation

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Full flow probes

o Minimal correction for pore pressure effects

o Greater bearing area

o Availability of simplified bearing capacity solutions

o Strong Irish influence internationally Boylan, Colreavy, O’Loughlin

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Advanced drilling rigs

www.geotech.se

o Multipurpose rigs for all drilling, in situ sampling and testing o Safety!

CPTU testing and

Sampling at NTNU’s

Stjørdal research site

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Shear Wave (S-Wave)

Particle motion is perpendicular to the direction of propagation (transverse).

Material returns to its original shape after wave passes.

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Shear wave velocity techniques

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MASW survey Ballinasloe

Lab bender elements

Vs values Irish soft soils

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Designed to give Vs / Gmax values Gmax = Vs

2

Not designed to give layers

Sample disturbance effects

• General

• Effects on clay

• Effects on intermediate soils / silts / laminated

soils

• Message: sampling disturbance effects can be

very pronounced and may not be conservative

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Sample disturbance effects in soft clay

Lad

d a

nd D

eG

root

(2

00

3)

o Stress path sampling to lab o Effect of drilling and tube sampling very pronounced. o Leads to: destructuration and loss of ‘. o UUC test will give very low su

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Sampling disturbance effects on clay

Lierstranda clay (Lunne et al, 1997a)

Reduction in pc`, M and cv at small strain e.g. M54 = 0.58 Mblock

Settlement overpredicted

Reduction in su, E at small strain. Increase in f and less strain softening e.g. su-54 = 0.78 su-block

Overdesign

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Sampling by the displacement technique

Displacement samples give higher stiffness, pc‘, su, etc but are less stiff post peak Design based on conventional and U4? MOSTAP 70 a possible way forward?

0

2

4

6

8

10

12

14

16

18

1 10 100 1000

Effective vertical stress (kPa)

Ax

ial s

tra

in (

%)

5deg displacement 4.64m

U4 3.69m

5deg conventional 3.6m

Denotes 'v0

Conventional v displacement

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Athlone brown laminated clay

o Block sample behaviour completely different o 5°, 30° and MOSTAP 65

destructured and densified o Poor sampling leads to non conservative design parameters o Similar finding for silts

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Sampling - conclusions

o Sampling in clay can destructure the material

leading to conservative design parameters.

o Sampling in silts and laminated soils can densify

the material leading to non-conservative design

parameters.

o Only the best available samplers should be used

(new tubes / sharp cutting edge / fixed piston)

o Less is more!

o Borehole effects? Try out MOSTAP 70?

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Undrained shear strength (su)

• su from lab tests

• su from CPTU

• su from full flow probes

• su from Vs

• su from field vane

• su from full-scale field trials / failures

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su - general

• Difficult parameter

o No unique value

o Anisotropy

o Test method

o su influenced by rate and temperature

o Effective stress / stress history:

o Norwegian clays CAUC: S = 0.3 and m = 0.7

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su from triaxial testing

• Clays only from SBT chart and / or Bq > 0.3

• Best samples only

• su/v0` = 0.3 consistent with SHANSEP for OCR 1

• su/v0`(DSS) = 0.22 for OCR 1

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su from CPTU

• Best quality su data only

• Good relationships especially for Nkt

• Fits well with Norwegian data

kt

vot

kt

netu

N

)(q

N

qs

u

02

u

uN

u-u

N

us

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su from Vs

• Logical to connect Vs to su

• Controlling factors the same, e.g. '

Norwegian clays L’Heureux and Long (2017)

DSS CAUC

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su versus Vs for Irish clays

Glacial tills su (CIUC) v Vs (MASW)

Soft clays su (DSS) v Vs

More work warranted, e.g. DSS

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Field vane testing – have we moved forward?

Photo courtesy Elmo Di Biaggo, NGI

0 50 100 150 200 250Time (s)

0

5

10

15

20

25

She

ar

str

ess (

kP

a)

Memovane test at 13m

Geonor vane borer

Envi - Memovane

Memovane test Onsøy

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su vane – Athlone / Portumna

Athlone

Portumna

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Full-scale field failures - Athlone

Trial embankment su/v' = 0.3-0.35 grey su/v' = 0.2-0.25 brown clay East abutment berm su/v' = 0.2-0.25 brown clay i.e. similar to lab and much higher than field vane

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Summary for su

• su is a complex parameter

• Irish soil behaviour consistent with world-wide

trends

• Useful data from CAUC, CAUE, DSS lab tests

• UU tests of no value and should be discontinued

• Field vane tests should be treated with caution

Modern equipment should be trialled

• Correlations with CPTU, full-flow probes and Vs

promising

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1D consolidation

• Theory

• Test types

• pc'

• Cc/1+e0

• Csec

• Correlations with Vs

• Surcharging (Ladd technique works well)

• cv

• Correlations with CPTU

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1D compression – IL oedometer test

Single increment – Terzaghi (1925)

tC

logsec

u

tc

u

z

ev

e2

2t

u

z

u

m

k ee

vw

2

2cv composite / complicated parameter

24 hour load increment

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IL oedometer - full test

• Onsøy Japanese sampler at

7.5 m

• Stress v , M, cv, Csec

• NB: Non linear nature of

M, cv, Csec

• pc` at min value of M, cv

(and max value of Csec)

(Janbu approach) Slightly

greater than Casagrande

• Need to know Cr/1+e0 (or M0),

pc‘, Cc/1+e0 and Csec

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IL or CRS?

o Drainage at top only so ub can be measured

o Faster tests o More data to produce smooth

curves

Conventional IL oedometers o Can we do shorter (<24hr)

tests? o Focus on primary or creep?

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Creep

Photo courtesy Fintan Buggy

Limerick Tunnel Approach Road (Alluvial clay / silt)

Arklow Bypass Avoca Valley Crossing (Alluvial deposits but very complex)

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Csec

wC 00018.0sec Simons (1974)

o sample disturbance effects (U100 samples obtained) o sample size effects (macro effects underestimated) o rate effects (much faster in lab than in field o Research warranted

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1D compression parameters from Vs

L’Heureux and Long, 2017

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M0 and pc`against Vs – Irish soils

o Encouraging fit o Local correlations necessary o More work well warranted

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Cc/1+e0

McCabe et al., 2014

cv composite / complicated parameter

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1D compression conclusions

• Reduce increment holding time in IL tests?

• More use made of CRS testing

• Use natural (+logv‘) scales to analyse data (e.g.

for pc‘)

• Cc well understood

• cv particularly complex and needs more work

(dissipation testing)

• Field creep seems to exceed that estimated for

lab. Try out modern “isotache” analysis technique

• Ladd approach to surcharge design seems to

work well

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Conclusions and recommendations

• Very significant developments since Eamon

Hanrahan’s 1979 book

• Experience has built on framework he introduced

• Considerable body of knowledge built up

• Work to be done / scope for introduction of

modern equipment and techniques

• Thanks for listening!

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River Shannon floodplain Athlone